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Prevalence of bruxism among Mexican children with Down syndrome

This study sought to determine the prevalence of bruxism in a Mexican community of children with Down syndrome, and to evaluate bruxism's relationship with age, sex, intellectual disability level, and type of chromosomal abnormality of trisomy 21. Using a cross-sectional design, 57 boys and girls (3 to 14 years old) were examined. Three approaches to establish presence or absence of bruxism were employed: parental questionnaire, clinical examination, and dental study casts. Data were analysed using bivariate analyses and conditional logistic regression. We found that the overall prevalence of bruxism was 42%. No statistically significant associations between bruxism and age, sex, or intellectual disability level were found. There was, however, a significant association between bruxism and type of chromosomal abnormality, with mosaicism being more frequently associated with bruxism.

López-Pérez, R, López-Morales, P, Borges-Yáñez, Maupomé, G, and Parés-Vidrio, G. (2007) Prevalence of bruxism among Mexican children with Down syndrome. Down Syndrome Research and Practice, 12(1), 45-49. doi:10.3104/reports.1995

Bruxism has been defined as a mandibular parafunctional behaviour[1] that is the
forcible clenching or grinding of the teeth, or a combination of both. Clenching the teeth is
the forceful closure of the opposing dentition in a static relationship of the mandible to the
maxilla in either maximum intercuspation or eccentric positions. Grinding the teeth is the
forceful closure of the opposing dentition in a dynamic maxillo-mandibular relationship as the
mandibular arch moves through various excursive positions[2]. While bruxism may occur
during the day or night, current polysomnographic and clinical studies have linked sleep-related
bruxism to sleep disorders[3]. Sleep bruxism occurs primarily during the rapid eye
movement phase of sleep[4]. The American Sleep Disorders Association defines bruxism
as a periodic, stereotyped movement disorder of the masticatory system involving tooth grinding
or clenching during sleep[5].

Social Factors:

Habits:

Combined etiological factors:

The aetiology and characteristics of bruxism are not well understood[6]. The causes
are
probably multifactorial and overlapping[2], and have been associated with several
factors (Box 1). Because of
different research methods, operational definitions, clinical criteria, and study populations,
the reported prevalence of bruxism varies in both adult and paediatric populations[2].
The prevalence in the general adult population has been reported between 3% and 90%[1,3,6-11].
Among children, prevalence ranges from 7% to 88%[1,3,6-14]. Previous studies[15,16]
have found that boys and girls without Down syndrome are equally likely to have bruxism, but one
recent study[14] posited that bruxism is more prevalent among boys.

Bruxism is considered a normal parafunctional pattern in the general paediatric population,
presumably associated with changes in dentition. Children who brux begin at about four to eight
years of age[6]. The incidence of bruxism is higher between 10 and 14 years of age,
decreasing afterwards[2,17]. The most commonly observed consequence from bruxism is
tooth wear, which can range from mild to severe wear facets - localised or generalised
throughout the dentition. Other consequences affect supporting tissues[1]: severe,
long standing bruxism may result in muscle hyperthropy (usually in the masseter, but also in the
temporal muscle)[18]. Reported consequences of sleep bruxism include headaches,
temporomandibular joint dysfunction, jaw pain, and pain when chewing[19,20].
Short-term acute therapy may involve physical therapy, nocturnal electromyographic biofeedback,
and medication to relieve anxiety and improve sleeping. Long-term management generally includes
some form of stress reduction, change in lifestyle, and an occlusal splint or night guard to
protect the teeth and masticatory system[21].

Few studies have investigated the prevalence of bruxism in children with Trisomy 21. Researchers
have reported prevalence figures between 18% and 70%[13,22-25]. When compared with
children without Down syndrome, investigators have found a higher prevalence of bruxism in boys
and girls with Trisomy 21[22,23,25], and it has also been suggested that daytime
bruxism is more common in children with Down syndrome due to spasticity[13]. However,
no study has reported if age, sex, intellectual disability level, and type of chromosomal
abnormality of the Trisomy 21 influence the prevalence of bruxism in the population with Down
syndrome. The objective of the present study was to characterise the factors associated with
bruxism in a group of children with Down syndrome.

Materials and Methods

Ethical implications

The study's design and conduct complied with the regulations for the protection of human
subjects stipulated by the organisations involved.

Environment

Using a cross-sectional study design, 86 children with Down syndrome studying at the John
Langdon Down Foundation in 1998 were recruited. The Foundation is a not-for-profit organisation
located in Mexico City that offers programmes delivering psychopaedagogical support and advice
to persons with Down syndrome and their families. To participate in this study, volunteers
provided verbal consent to an oral examination, including dental impressions. Their
guardians/parents provided written consent.

Of the 86 students, 29 were excluded from the study due to unsigned consent forms, or because
they had ongoing maxillary orthopaedic or orthodontic treatment, were wearing oral prostheses,
or because of assorted conditions such as epilepsy, autism, or cerebral palsy. The study group
therefore included 57 children. No dental treatment was offered or carried out as part of the
invitation to participate, but participants and guardians were given a summary of the oral
health status findings for their treating dentist, if desired. No radiographs were taken.

Variables collected

We diagnosed bruxism using a questionnaire, intraoral examination, and dental study casts. A
history of bruxism included grinding or clenching (day or night) as reported by parents through
a questionnaire, while clinical indicators were the presence of dental wear facets in one or
more primary and/or permanent teeth. The presence of wear facets detected during the intraoral
examination was confirmed in the dental study models.

The parental questionnaire also provided information regarding medical history and medication.

The intraoral examination was administered under artificial light with the patient lying down.
The teeth were dried with cotton rolls and each tooth was examined using a No. 5 flat dental
mirror. Standardisation was carried out by examining 20 patients, not included in the study
population, on two occasions. The kappa value (intraexaminer variability) obtained by a
calibrated paediatric dentist (PLM) was 0.98.

Dental impressions were taken with alginate to make dental study casts (one upper and one lower
plaster model). Again, the same clinical examiner performed standardisation training by
evaluating 20 casts of patients not included in the study population, and re-examined them 15
days after the first examination. In this case, the kappa value (intraexaminer variability) was
also 0.98.

Age

Boys with bruxism

Girls with bruxism

Total with bruxism

(years;months)

n

f

(%)

n

f

(%)

n

f

%

3;00 - 5;11

4

0

0

3

2

67

7

2

29

6;00 - 8;11

13

6

46

9

6

67

22

12

59

9;00 - 11;11

11

5

46

7

4

57

18

9

50

12;00 - 14;11

6

1

17

4

0

0

10

1

10

Total

34

12

35

23

12

52

57

24

42

Table 1 | Prevalence of bruxism by age and sex in a population with Down syndrome.n = number of
children examined. f = frequency. Difference between age subgroups: χ2 = 5.50,
p = 0.36 Difference between sexes: χ2 = 0.00,
p =
1.00

The control variables were sex (male or female), age (years and months), severity of
intellectual disability measured by special educational needs (mild, moderate, or severe) (as
per the John Langdon Down Foundation needs' assessment that structures the curriculum at the
individual level), and the type of Trisomy 21 chromosomal abnormality (regular, mosaicism, or
translocation, as per the medical history chromosomal studies). This information was obtained
from each child's medical history and the educational programme.

Statistical analysis

We used SPSS version 9.0 for data analysis. The chi-square test (χ2) was employed to
determine if there were statistically significant differences among subgroups according to age,
sex, intellectual disability level, and type of chromosomal abnormality.

Age and sex distribution: there were 34 boys (60%) and 23 girls (40%). Age range was 3.0-14.1
years old (mean age 8.67 years ± 2.96). Bruxism was diagnosed in 24 of the 57 children (42%).

Prevalence of bruxism by age and sex

Bivariate analyses. As shown in Table 1, there was no significant difference in the prevalence of
bruxism when children were arbitrarily divided into four age subgroups (χ2 = 5.50,
p = 0.36). This habit was most common in the 6;00 to 8;11 year age group, with bruxism
decreasing in frequency in the older group. There was no significant difference in the
prevalence of bruxism when compared by sex, where 12 boys (35%) and 12 girls (52%) were bruxists
(χ2 = 0.00, p
= 1.00).

Prevalence of bruxism by intellectual disability level

Type of chromosomal abnormality

n with bruxism

n

f

(%)

Regular

36

12

33

Mosaicism

11

8

73

Translocation

5

2

40

Total

52

22

42

Table 3 | Prevalence of bruxism by type of chromosomal abnormality in a Mexican paediatric group
with Down syndrome. n = number of children examined.
f = frequency. Difference between type of chromosomal abnormality subgroups: χ2 = 6.91;
p =0.032

Bivariate analyses. Intellectual disability was measured by special education needs.
Table 2 shows that there was no
significant difference among children with different levels of special education needs (χ2
= 4.53, p
= 0.10).

Prevalence of bruxism by type of Trisomy 21 chromosomal abnormality

Bivariate analyses. The type of Trisomy 21 was known in 52 individuals. As shown in
Table 3, children with mosaic trisomy had the highest bruxism prevalence (χ2 = 6.91,
p =
0.03).

Multivariate logistic regression model

Table 4 presents results derived from a
conditional logistic regression model (stepwise) incorporating the four independent variables.
Children with Down syndrome with mosaicism had five times higher probability of having bruxism
than other children with Down syndrome.

Discussion

Variables

Significance (p)

Odds ratio

95.0% C.I.

Lower

Upper

SEX male

0.08

0.31

0.084

1.13

CA regular

0.10

-

-

-

CA mosaicism

0.03

6.03

1.18

30.77

CA translocation

0.82

1.26

0.17

9.35

Constant

0.94

1.04

-

-

Table 4 | Model of logistical regression controlling: sex, chromosomal abnormality (CA), special
education needs, and age in a Mexican paediatric group with Down syndrome.Variables entered on
step 1: sex, chromosomal abnormality, special education needs, and age.

The present study confirms the strength of the association between signs and history of tooth
grinding in children with Down syndrome and some of the more salient features that characterise
subgroups of children with this disability. We found a fairly high percentage of this behaviour
(42% prevalence) in the community studied - with age modifying the experience. When contrasted
with other reports in the literature, we found that the prevalence was much higher in other
places - Gullikson[22] reported a prevalence of 79% in 28 American children with Down
syndrome between 3-10 years old; Alarí[13], 70% in 21 Spanish children (age range, 6
to 7 years); Bell et al.[25], 67% in 49 Australian children; and Borea et al.[23],
45% in 37 Italian children (mean age, 12 years old). Only Hernández et al.,[24]
reported lower figures - again in a Mexican population - 18% in 61 children (range 6 to 14
years). The different ages in the various study populations might account for the observed
discrepancies.

The latter speculation gains strength when considering changes across age groups in the present
study. As we were limited to a cross-sectional design, we cannot draw conclusions in terms of
longitudinal trends. But we may contrast different age groups, and venture some explanations
that may be relevant to developmental changes along the age continuum. When comparing the
prevalence of bruxism by age subgroups, the children examined in this study exhibited similar
patterns of bruxism to those found in the general paediatric population - the highest prevalence
of this parafunction was found in the subgroup of children between 6;00 to 8;11 years.
Prevalence decreased in the older age groups. In the general population, the frequency of
grinding appears to increase up to age 7[8], but other authors indicated that
prevalence is at its highest between 10 to 14 years of age[2]. Most investigators
agree that bruxism increases during the mixed dentition stage[8], and decreases with
age[2,8,17], even though some reports disagreed with these interpretations, based on
their findings of similar prevalence of bruxism in teenagers and adults[9], and
similar prevalence in children with and without mixed dentition[26].

Compounding the trends identified for age and sex also provided interesting contrasts. Our
findings concurred with studies which found no significant prevalence differences between boys
and girls (3 to 17 years of age[15,16], but disagreed with the higher prevalence in
boys reported by Shetty and Munshi[14]. Future research might address this seemingly
conflicting pattern of findings by carefully controlling for tooth eruption/shedding variation
across sexes, which may be the crux of these reported differences, or a contributing factor.

The only other study to address intellectual disability levels in relation to bruxism is the
investigation reported by Borea et al.,[23]. They examined patients with Down
syndrome with intellectual disability from mild to severe and, just as we found, there appears
to be no association between these two variables.

Some methodological limitations apply to the present study. Results cannot be extrapolated to
the overall population with Down syndrome in Mexico, in particular because this is a highly
detailed study in a small, well-defined population, but also because no reliable Down syndrome
national figures are available. Furthermore, the student population at the John Langdon Down
Foundation probably represents a population who have highly-structured, well-documented
educational and medical programmes that meet their needs. Other children with Down syndrome may
have less advantageous oral health or educational situations or diagnoses. More relevant to the
design aspects of the present study is a methodological limitation that has plagued studies in
the past - how to diagnose bruxism. The errors expected when using a questionnaire or an
interview to collect information about bruxism tend to underestimate or overestimate the
incidence. Although dental wear can be objectively measured, this might not indicate the current
level of bruxism because individuals who bruxed in the past may present with dental facets,
while subjects who recently began bruxing may not yet have signs of dental wear[27,28].
While the reliability tests in some studies have shown acceptable variability[27], a
minority of authors have indicated that the use of polysomnographic cut-off criteria to
discriminate the presence or absence of sleep bruxism should be an integral part of the
diagnostic procedure[3]. In the present study we met this challenge by diagnosing
bruxism only when positive reports were gathered through the questionnaire, the intraoral
examination, and the analysis of dental models. We suggest that this three-pronged approach
constitutes as validated a criterion as may reasonably be attained.

In summary, the present study found that children with Down syndrome between 3;00 to 14;11 years
old had a 42% prevalence of bruxism. The prevalence of bruxism was not different for boys or
girls, was similar to that reported in the general paediatric population, and was more frequent
in children 6;00 to 8;11 years old. Furthermore, intellectual disability levels had no apparent
relationship to the experience of bruxism. There was a significant difference, however, across
the different types of Trisomy 21, with mosaicism being the type that had the higher prevalence.

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